(1) Field of the Invention
This invention relates to a shotgun cartridge and assembly for firing, and more particularly to a sabot-retaining shotshell cartridge, shotgun chamber, and barrel or barrel insert configured to fire the shotshell cartridge.
(2) Description of the Related Art
The use of slugs with shotguns is intertwined with the history of shotguns themselves. U.S. Pat. No. 3,726,231 discloses a waisted slug known as the BRI slug or bullet. Such waisted slugs grew to prominence in the 1970's and 1980's. That period saw increased interest in use of shotgun slugs motivated by a combination of user preference and regulatory influence. The availability of rifled shotgun barrels also increased, further enhancing slug performance and increasing the use of saboted projectiles. In parallel, the field of muzzle-loading rifles has flourished with a dedicated following. Saboted projectiles may also be used with muzzle-loading rifles.
There are ongoing development efforts in saboted projectile technology. U.S. Pat. No. 5,214,238 discloses a sabot for chambering conventional bullets in a shotgun. U.S. Pat. No. 5,415,102 discloses a muzzle loading sabot. General dimensions of shotshell cartridges and pistol bullets are respectively disclosed in American National Standard Voluntary Industry Performance Standards for Pressure and Velocity of Shotshell Ammunition for the Use of Commercial Manufacturers and in Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Pistol and Revolver Ammunition for the Use of Commercial Manufacturers ANSI/SAAMI Z299.2-1992 and Z299.3-1993 (American National Standards Institute, New York, N.Y.).
Sub-caliber projectiles in shotshells or shotshell cartridges are desirable to increase velocity levels, improve ballistic coefficients, and flatten the trajectory of the bullet path. Many varieties of sabots, e.g., one-piece, multi-petal, or two-piece, are currently used in shotshell cartridges for sub-caliber projectile applications. Existing sabot designs typically suffer from at least one of two problems: 1) excessive ejecta weight and 2) accuracy issues. Prior art designs, which include bulky sabots, over powder cups, and various spacer wads, typically significantly increase ejecta weight. Higher ejecta weight reduces the velocity level that may be achieved. Higher ejecta weight also contributes to greater recoil energy felt by the shooter for a given velocity level. In spin-stabilized systems, the sabot must locate the sub-caliber projectile precisely in the center of the bore and the projectile/sabot separation at muzzle exit must not induce any unbalanced forces on the projectile. Using known designs, these criteria may be very difficult to achieve consistently, resulting in degraded accuracy as compared to the same projectile fired in a non-sabot system. These problems become more pronounced as the difference between the sub-caliber projectile diameter and bore diameter increases, which restricts the use of more efficient, smaller-caliber projectiles.